Dairy cattle operations require efficient breeding regimens for optimal performance and economic yield. Milk production is dependent on cows in the operation becoming pregnant, giving birth and lactating. After birth a cow can be milked for over two hundred days. However, after about 150 days post parturition, the amount of milk produced begins to fall off rapidly. Thus, minimizing the period of time between calving and the beginning of the next pregnancy increases the value of the cow to the dairy operation.
Moreover, the economic value to a dairy operation of a typical cow decreases rapidly thirty six months after first calving. Increasing the number of pregnancies that a cow has during this time maximizes the return on investment in the animal in terms of feed, overhead and other costs.
In recent years, several hormone products have come on the market for manipulation of the estrus cycle in cows. These products include gonadotropin releasing hormone (GnRH), lutenizing hormone LH, prostaglandin F2α, estrogen, progesterone and synthetic analogs of certain of these hormone. Each of these products are used at various times in the estrus cycle to encourage ovulation or otherwise aid in conception and maintenance of pregnancy.
Progesterone levels may elevated in cows by use of exogenously applied progesterone and used, for example, to synchronize estrus in a herd. Application or treatment is conveniently done using a vaginal insert that is constructed to release progesterone at a steady rate. The EAZI-BREED™ CIDR® is produced by DEC International, NZ Ltd. and available in the U.S. from Pfizer Animal Health Products (New York, N.Y.). The CIDR insert is indicated for protocols that allow for synchronization of the a cow's estrus cycle thereby giving the dairy cattle operation a better chance of detecting heat in the cows by narrowing the window in which to place the cow under increased scrutiny. Indeed, the protocols for which the CIDR insert are approved require heat detection to determine optimal time for artificial insemination. For example, in the FAST BACKSM method for lactating dairy cows, a cow undergoes artificial insemination and a CIDR insert is administered fourteen days later. At Day 21, the CIDR is removed and the animal is observed over Days 22-25 for heat detection and inseminated on observation of heat. However, use of prostaglandins (such a LUTALYSE®) are contraindicated in this protocol.
Unfortunately, heat detection is difficult, requires proper training and experience to do correctly and is time consuming for the operator and employees in a dairy operation. Some authorities recommend observation of the animals at least three times daily. Certain signs of heat, such as standing heat, may only be present for ten hours within a single estrus cycle. Many signs of heat are also subtle and easy to miss. Large dairy operations often employ many unskilled workers who do not have the necessary training to carry out heat detection. Some estimates place failure of heat detection at or higher than 50%. Missing an observed heat means another estrus cycle must occur before breeding can be attempted again.
Some methods, such as the Ovsynch method have proposed estrus cycle modification using certain hormone injection regimens and the elimination of heat detection. However, at least one evaluation of the Ovsynch method has shown that the method does not give acceptable rates of conception using a fixed-time artificial insemination without heat detection. See, e.g., “Reproductive Management of Dairy Heifers” by Paul M. Fricke, Ph.D. of the Department of Dairy Science, University of Wisconsin-Madison.
Thus, a method is needed to ensure increased breeding efficiency with reduction in the number of months in the breeding cycle without the need for heat detection prior to breeding.